1. Field of the Invention
The present invention relates generally to devices for converting a wavelength of light into a harmonic, and more particularly to improvements in an optical wavelength converting device including an optical waveguide of a thin organic film and a method of manufacturing the device.
2. Description of the Background Art
Recently, in the field of optoelectronics, a device for converting a wavelength of light into a harmonic employing a nonlinear optic effect has been extensively studied. Such an optical wavelength converting device can be employed, for example, for converting a wavelength of laser light into a harmonic.
One of wavelength converting devices, known to those skilled in the art, is of a bulk crystal type which requires a monocrystalline material having birefringence to obtain phase matching. Meanwhile, the devices of optical waveguide type and optical fiber type are also known which can obtain phase matching without a material having the birefringence. However, as for a waveguide-type wavelength converting device including a waveguide layer formed on a substrate, the waveguide layer should be accurately controlled to have a suitable thickness to obtain the phase matching.
It has been understood in general that organic materials have a higher nonlinear coefficient than inorganic materials, and thus the wavelength converting device including a waveguide layer of an organic material can have a wavelength conversion efficiency several hundred times larger than that of the one including a waveguide layer of an inorganic material.
Japanese Patent Laying-Open No. 62-75425 (1987), for example, discloses a wavelength converting device including an optical waveguide layer formed of an LB film of a nonlinear organic material formed on a substrate by an LB (Langmuir-Blodget) technology. The mechanism of generation of harmonics in the waveguide layer of the nonlinear organic material is, for example, described in detail in "Journal of Molecular Electronics", Vol. 1, 1985, pp.25-45 by J. Zyss. Further, the LB technology is, for example, described in detail in "Journal of Molecular Electronics" Vol. 1, 1985, pp. 3-17 by M. Sugi. The LB film has its thickness accurately controllable relatively easily.
The wavelength converting device of the related art includes the waveguide layer of the LB film having a definite thickness controlled to obtain phase matching with respect to an input laser beam having a specific wavelength. Therefore, the wavelength converting device designed for the input laser beam with a specific wavelength cannot be employed for another input laser beam with a different wavelength.
Meanwhile, in an erasable optical disk employing a photochromic material, a write laser beam and a read laser beam with different wavelengths to each other are sometimes employed. Two wavelength converting devices are required in converting in wavelength for these two laser beams with different wavelengths.